Hello again! This week we had a much lighter assignment 🙏🙏, 3D printing an impossible object.
I began on Thingiverse, searching for a somewhat embarrassingly long time. I used keywords such as “articulated,” “hinges,” “spring,” “button,” and “switch,” trying to find objects with moving parts that would be fun to manipulate, whilst being impossible to manufacture by other means. I had two candidates:
The Springy Bunny (by 3DP_PARK):
I really liked this design and the video demonstration on Thingiverse made me chuckle. I also imagined it’d be very fitting for the gumball capsule. One small issue I had was that it didn’t include hinges/interlocking features, moving parts (kinda?), internal geometry, or high complexity, as required by the assignment description. As a result, I opted for candidate two:
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The Print-in-Place Fidget Cube (by mathgrrl):
This design fit the impossible description :). I sent it to the Bambu printer scaled at the approximate size of the gumball capsule, and foudn two issues: the hinges were unsatisfying, both visually and tactile-y, and the hinges were poor quality. One of the hinges came out and the cube became more of a blocky snake.
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So I found a new design:
The Fidget Cube High Quality Hinge (by Wultz):
The object had two files: one with a lower tolerance and one with a higher tolerance, meant for printers that can achieve 0.1-0.15 mm layer heights. Obviously, I went for the tighter tolerance, confident in the technological prowess of the Bambu X-1 Carbon. The previous cube was a little small so I increased the side-length to be 40 mm total, which was slightly smaller than the diameter of the capsule.
Disaster! It wouldn’t fit in the capsule at all. Outside of this though, the Bambu didn’t disappoint, and the cube had very nice hinges. I gave it to a fellow EDES 210 classmate as a gift and reprinted with a side-length of 32 mm.
Tada 🙂 perfect fit. It doesn’t even wobble if you shake the capsule. I wet-sanded each cube and placed them within their capsules with the printed info slip.
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The happy saga ends here. Onto the SLA print.
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I naively used the same file, confident of its success due to the Formlabs printer’s capabilities of super thin layers. I felt .1 mm was plenty small, and sent it to be printed with clear resin. After two and a half hours, a ten minute bath, and a thirty minute cure, I was left with these (after removing supports):
Two blocks, fused completely solidly together. I tried using a box cutter to separate each face, but it made very little progress. I decided to reprint the part, with some modifications.
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This time, I would use the higher tolerance file, which had larger gaps between each face. I still had to shrink the model down to about 88%, which reduced these spacings, so to compensate I used a 0.05 mm layer height, a move that would cost me an extra hour. After three and a half hours, a fifteen minute bath, and a thirty minute cure, I was left with these (before removing supports).
Two blocks, fused completely solidly together (getting some deja vu?). Since I felt I maybe saw a gap between the faces when moving the part to the wash, I thought that the part was still salvageable with some cuts. Five minutes with the box cutter gave minimal results. I took the part to the bandsaw, cutting all the way up to each hinge. Once I did so, I flexed the hinge, and it bent perfectly.
I lied. It snapped, and upon inspection, there wasn’t even a hinge gap. Absolutely no hinge geometry outside of the surface. Complete solid, clear, beautiful resin. I tried a couple other faces with the band saw to see if it was a fluke, but no. Every hinge was fused shut.
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Plan D: New file.
As I write this blog at 1 AM on a Monday morning, our last print chugs along within the Formlabs printer, assumed perfect layer by perfect layer. I used a different model this time, the “Failproof Fidget Cube with improved hinges” by DrDigital (I mean, it has failproof in the name!). A bit after I started this print, I read a blogpost from a fellow EDES 210 student who happened to try this very object, only for its articulated hinges to tragically fuse on the resin print. I am losing hope. Sorry for using this much resin. End communication.
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BROADCAST – 3:01 AM – OEDK FIRST FLOOR
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I have bad news.
I have bad news.
No more attempts. I’ve learned my lesson (though it shouldn’t have taken this long). SLA resin bad for articulated joints or moving parts. Design must be super aware of joint tolerances if considering SLA. I sawed two of the cubes in half so they could fit in the capsule and called it a night. Or morning, I suppose.
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Cost Analysis:
Labor: 3 hours active (though up to 17 hours inactive sitting at the OEDK, waiting and working) (at $10 an hour): $30
Material:
White PLA ($19.99 for 1kg Roll at ~200g): $4.00
V4.1 Clear Resin ($159 for 1L [wow] at ~210 ml ): $33.39 (I’m really sorry)
Sum Total: $67.39, averaging $13.48 per cube. Definitely getting your 25¢ worth at the gumball machine.
Cleaned Workspace
